| Obsideo AS | | 2020 |
| Octen AS | Real estate | 2020 |
| Odd Fellow Ordenshus Hamar AS | Real estate | 1960 |
| Odd M Ødegaard AS | Real estate | 1973 |
| Odessa Partner AS | Professional & scientific | 2009 |
| Odessa Partner Ltd Nuf | Professional & scientific | 2006 |
| Offshore Wind Design AS | Professional & scientific | 2021 |
| Ofstad Eiendom Hamar AS | Real estate | 2010 |
| Ofstad Holding AS | Real estate | 2020 |
| Okka Holding AS | Financial services | 2010 |
| Ola Christiansen AS | Construction | 2017 |
| Ola Erik Molstad AS | Transport & logistics | 1989 |
| Ola Stenberg Invest AS | Information & communication | 2021 |
| Old Grumpy Barber AS | Other services | 2024 |
| Ole Fredrik Holding AS | | 2022 |
| Olrud Eiendom AS | Real estate | 2007 |
| Olrud Invest AS | Real estate | 2005 |
| Olsen & Berge Holding AS | Real estate | 2024 |
| Omb 138 Holding AS | | 2023 |
| Omega Finansrådgivning AS | Financial services | 1997 |
| On Edge AS | Other services | 2016 |
| One Door AS | | 2024 |
| One Piece Sushi AS | Hospitality | 2025 |
| Onsite Security AS | Administrative & support | 2019 |
| Onsite Technologies AS | Administrative & support | 2025 |
| Onway AS | Arts & recreation | 2022 |
| Oplandske Eiendom AS | Real estate | 2004 |
| Oppgradert Bad AS | Construction | 2023 |
| Oppland Fylkeskraft AS | Public administration | 2007 |
| Optiker Ottestad AS | Wholesale & retail | 1996 |
| Optilaser AS | Wholesale & retail | 2012 |
| Orona Norway AS | Construction | 2002 |
| Oscars Gate 11 AS | Real estate | 2022 |
| Osilion AS | Information & communication | 2024 |
| Osint Analytics AS | Information & communication | 2005 |
| Oslo Frimerke- Og Myntauksjoner AS | Wholesale & retail | 2022 |
| Oslopaviljongen AS | Real estate | 1993 |
| Oss I Mellom AS | Wholesale & retail | 2024 |
| Otr Invest AS | Financial services | 2005 |
| Oustad AS | Wholesale & retail | 2024 |
| Out of Bounds Hamar AS | Administrative & support | 2021 |
| Ove AS | | 2026 |
| Ove KR. Hafsås Invest AS | Real estate | 2007 |
| Overseas Capital Group Inc | Real estate | 1999 |
| P&M Invest AS | Information & communication | 2024 |
| P.G Mattsson AS | Health & social care | 2022 |
| P.J.J. Holding AS | Other services | 2005 |
| Pa Nyhagen AS | Wholesale & retail | 2013 |
| Padel Red Hamjern AS | Administrative & support | 2017 |
| Padel Red Kolltjern AS | Arts & recreation | 2020 |
| Pah 17 AS | Real estate | 2021 |
| Pandu AS | Information & communication | 2023 |
| Parkgata 12 AS | Real estate | 2023 |
| Parkgata 13 AS | Real estate | 2019 |
| Parkgata 32 AS | Real estate | 2022 |
| Parkgata 36 Reorg AS | Real estate | 2021 |
| Parkgt 24 AS | Real estate | 1998 |
| Pathfinder Holding AS | Wholesale & retail | 2013 |
| Pba Holding AS | Financial services | 2014 |
| Ped Data AS | Education | 1988 |
| Pedersen Rud & Larsen Eiendom Da | Real estate | 2001 |
| Peer Gynt Kjøpesenter AS | Real estate | 1990 |
| Pegus Møbler AS | Wholesale & retail | 1975 |
| Pegusgruppen AS | | 1994 |
| Pegusgruppen Eiendom AS | Real estate | 2018 |
| Pekas Holding AS | Real estate | 2014 |
| Pelsdyrfôr Hamar SA | Wholesale & retail | 1947 |
| Pengeråd AS | Professional & scientific | 2014 |
| Pepling AS | Information & communication | 2009 |
| Per Lund Invest AS | Administrative & support | 1987 |
| Perito AS | Information & communication | 2021 |
| Petersen Og Skogheim Servicesenter AS | Other services | 2002 |
| Petter Antonsen Invest AS | | 2019 |
| Petters AS | Real estate | 2019 |
| Pettersen VVS & Industriservice AS | Construction | 2026 |
| PH Service AS | Construction | 2017 |
| Philip Orseth Eiendom AS | Real estate | 2019 |
| Phrontech AS | Information & communication | 2025 |
| Phrontech Holding AS | | 2025 |
| Piamo AS | Information & communication | 2024 |
| Pinnerud Handelsbygg AS | Real estate | 2024 |
| Pinto Thai Takeaway AS | Hospitality | 2024 |
| Pivot Holding AS | | 2025 |
| Pkkm AS | Construction | 2005 |
| Plan B Eiendom AS | Real estate | 2009 |
| Podium Hamar AS | Other services | 1997 |
| Polefitness Hamar AS | Education | 2020 |
| Politia AS | Information & communication | 2019 |
| Port Innlandet AS | Construction | 2024 |
| Powerplay Club Limited Nuf | Arts & recreation | 2010 |
| PPC AS | | 2025 |
| PRH Holding AS | Arts & recreation | 2021 |
| Primary Care Services AS | Health & social care | 2023 |
| Printex Trykkeri AS | Manufacturing | 1996 |
| Pro Media Concept Da | Administrative & support | 2000 |
| Problemhjelpen Da | Manufacturing | 2008 |
| Produce AS | Arts & recreation | 2024 |
| Professo AS | Hospitality | 2012 |
| Professor Hansteensgate 88 AS | Real estate | 2019 |
| Progress Interactive AS | Information & communication | 2016 |